The present invention relates generally to the generation of hydraulic pressure in a vehicle brake system. In particular the invention is geared to a hydraulic pump comprising at least six cylinder/piston arrangements.
Modern hydraulic or electrohydraulic vehicle brake systems require reliable pressure generators in order to be able to implement safety-relevant functions such as antilock brake control or traction control. In the case of these functions a hydraulic pressure for controlling one or more wheel brakes is generated by means of the pressure generator.
Such a pressure generator is known for example from WO 2006/061178 A1, and corresponding U.S. Patent Application Publication No. 2008/191549A1, both of which are incorporated herein by reference. The pressure generator comprises a piston pump as well as an electromotive actuator for actuating the piston pump. The piston pump possesses a housing, in which a plurality of cylinder bores for receiving one pump piston each are formed.
Depending on the form of construction, the piston pump described in WO 2006/061178 A1 comprises 5, 6, 8 or more cylinder/piston arrangements. In the case of a multi-circuit vehicle brake system, the individual cylinder/piston arrangements may be divided into a plurality of sets and each set may be associated with one hydraulic circuit each. In this case, the more cylinder/piston arrangements provided per set, the lower the pressure pulsations arising during control interventions and hence the greater the operating comfort.
From WO 99/64283 and corresponding U.S. Pat. No. 6,446,435 B1, both of which are incorporated herein by reference, it is known to provide one set of three cylinder/piston arrangements per hydraulic circuit. The three cylinder/piston arrangements of each hydraulic circuit are in this case disposed in a star-shaped manner within one plane. The two planes thus arising are disposed parallel to one another and penetrated at right angles by a common eccentric shaft. The electromotively driven eccentric shaft interacts in a known manner with the pistons preloaded in the direction of the eccentric shaft in order to deliver hydraulic fluid to the wheel brakes or away from the wheel brakes.
The underlying object of the invention is to prolong the service life of the known multi-piston pumps whilst maintaining the operating comfort.